Conversion of a hip fusion to a total hip arthroplasty (THA) is a technically demanding procedure with variable outcomes and should not be undertaken without careful consideration by both the surgeon and the patient.
The most common indications for conversion of an arthrodesed hip include malposition, pseudarthrosis, ipsilateral knee pain, and disabling low back pain.
Patients may also seek conversion related to the disability associated with an immobile hip or before undergoing an ipsilateral knee replacement.
Important technical considerations include adequate exposure, removal of hardware if present, careful identification of bony landmarks to ensure proper implant orientation, and maintenance or restoration of hip biomechanics.
Surgical exposure is often dependent on the fused hip position, boney anatomy, and presence and location of hardware but commonly requires a more extensile approach.
Acetabular bone quality may be poor, and when uncemented cups are used, supplemental screw fixation is commonly needed.
Hip fusion takedowns can provide significant improvement in pain and function for patients with good survivorship at 10 years but generally do not achieve the same reliable outcomes as primary THA (Table 19.1).
The best outcomes are seen in patients whose abductors have not been violated during the hip fusion and in patients with a spontaneous arthrodesis.
Patients with poor abductor function after surgery may become cane dependent for life.
Routine hip retractors
Metal cutting burr
Hardware removal instruments
Broken screw removal set
In addition to an uncemented acetabular component, in cases with distorted anatomy or significant bony defects, autogenous bone graft from the arthrodesis site, supplemental screw fixation, and metal augments may be required.
On the femoral side uncemented femoral components most commonly are used. Proximal fixation may be used if the metaphyseal bone is of good quality and there is no significant proximal femoral deformity requiring correction. Distal fixation is preferred if the proximal metaphyseal bone is distorted or significantly compromised by a deformity or prior hardware.
Table 19.1 ▪ Ten-year Survivorship After Hip Fusion Conversion to Total Hip Arthroplasty
No. of Hips
Age at Conversion (Range) (y)
Follow-up Years (Range)
Spontaneous Versus Surgical Fusion
Ten-year Survivorship (%)
Kilgus et al. (1990)
Higher failure rate in the surgical fusion patients
Joshi et al. (2002)
Spontaneous fusion had better functional results
Richard et al. (2011)
Transtrochanteric or direct lateral
Fernandez-Fairen et al. (2011)
Anterolateral (21); transtrochanteric (15); posterolateral (12)
18 spontaneous; 30 surgical
Large-diameter femoral heads (36 mm or larger) in combination with ultrahigh-molecular-weight polyethylene liners are the preferred bearing surface. Dual mobility constructs may also be considered, particularly when there are abductor deficiencies or severe spine degeneration and deformity.
If a posterior, anterolateral, or transtrochanteric approach is planned, the patient is placed in a lateral decubitus position, which allows for a more extensile exposure if needed.
A supine approach may be used if a direct anterior approach is preferred or required to remove anteriorly placed or intrapelvic hardware.
Draping should allow for adequate access to the proximal pelvis and entire femur.